This section provides background information related to the present disclosure which is not necessarily prior art.
During combustion in a diesel engine, an air/fuel mixture is delivered through an intake valve to cylinders and is compressed and combusted therein. After combustion, the piston forces the exhaust gas (i.e., the exhaust stream) to flow from the cylinders through an exhaust system, from which the exhaust stream is released to the atmosphere. The exhaust stream may contain oxides of nitrogen (NOx) and carbon monoxide (CO).
Exhaust stream treatment systems may employ catalysts in one or more components configured for accomplishing an SCR process such as reducing nitrogen oxides (NOx) to produce more tolerable exhaust constituents of nitrogen (N2) and water (H2O). Reductant may be added to the exhaust stream upstream from an SCR, and, for example only, the reductant may include anhydrous ammonia (NH3), aqueous ammonia or urea, any or all of which may be injected as a fine mist into the exhaust stream. When the ammonia, mixed with the other constituents of the exhaust stream, reaches the SCR component, the NOx emissions within the exhaust stream are broken down. A Diesel Particulate Filter (DPF) may then capture soot, and that soot may be periodically incinerated during regeneration cycles. Water vapor, nitrogen and reduced emissions exit the exhaust system.
To maintain efficient NOx reduction in the SCR component, a control may be employed so as to maintain a desired quantity of the reductant (i.e., reductant load) in the SCR component. As the exhaust stream, containing NOx, passes through the SCR component, the reductant is consumed, and the load is depleted. A model may be employed by the control to track and/or predict how much reductant is loaded in the SCR component and to maintain an appropriate reductant load for achieving a desired effect such as reduction of NOx in the exhaust stream.
California Air Resources Board (CARB) regulation requires for application equipped with selective catalytic reduction (SCR) to detect a system malfunctioned/deterioration (e.g. urea injection) that leads to improper urea delivery that would cause a vehicle's NOx emissions to exceed the regulated emission levels. Accordingly, it is desirable to provide a robust method and system for monitoring reductant delivery performance for an SCR catalyst.